The present invention relates generally to an impact attenuation liner assembly for a protective helmet, such as a fire helmet, and to a protective helmet including such a liner assembly.
There are known in the prior art fire helmets which include liner systems for absorbing forces such as might be encountered during fire fighting activities. For example, U.S. Pat. No. 4,286,339 discloses a fireman's helmet having an outer shell, an inner liner and a plastic rim which encases the lower portion of the inner liner. The inner liner is molded from a non-resilient foam material, such as polyurethane. Associated with the inner liner is a cradle of radially disposed web straps. The straps are joined together at the central apex of the cradle and extend downwardly to the annular rim. Each strap passes beneath the annular rim and proceeds upwardly along the outer surface of the annular rim, wraps about a tube inset in a groove in the outer surface of the inner liner, and then proceeds under the annular rim to approach the apex as a free end. The free ends of the straps are secured to a draw string which is knotted to allow adjustment of the size of the cradle.
Apex impact forces occurring on the referenced helmet can cause the web straps to stretch, flatten the tube about which the straps are wrapped, and deform the compressible, non-resilient inner liner. Deformation of the non-resilient foam liner will likely result in permanent damage to the liner, which may prevent further use of the liner. Furthermore, the polyurethane liner, if exposed to high temperatures, will expand. Such expansion may cause the liner to crack and may also cause the inner liner to push itself out of the outer shell. Thus, this liner is essentially a "single use" liner since it cannot be reused if expansion of the liner occurs during use in a high temperature environment, or an impact force of sufficient magnitude impinges on the helmet causing permanent deformation of the foam liner. A further disadvantage of the liner is the plastic rim, which adds weight to and increases the cost of the helmet.
Accordingly, there is a need for an improved impact attenuation liner assembly for a protective helmet wherein the liner assembly includes an impact cap formed from a resilient, heat-resistant material.